You used a rat tunnel [Bronze / 10G]
You stayed in possession of others for most of a 3 minute period [Bronze / 10G]

First of all you need to get 3 runes and acquire the "Possession" skill. Runes can easily be found when equipping the "Heart" skill.
Search for a rat tunnel and possess a nearby rat. Entering the tunnel will earn you the Creepy Crawly trophy / achievement.
The possession cannot end while you are inside the rat tunnel. Just wait for 3 minutes before you move on. The Inhabitant trophy / achievement will pop once you transform back to your human form.